Sterilization of evaporated milk in glass containers



Patented 1945 STERIIJZATIONOF EVAPORATED MILK IN GLASS CONTAINERS Randall Whitaker, Robert P. Myers, and Robert E. Homberger, Baltimore, Md, alsignors to Sealtcst, Inc., Baltimore, Md, a corporation of 1 Maryland Application July 22, 1942-, Serial No. 451,814

4 Claims. (01. 90-214) This invention relates to improvements in the preparation of evaporated milk and relates more particularly to methods of sterilizing evaporated milk in glass containers.

The public has always been accustomed to Durchasing evaporated milk in tinned cans. Al-

, though entirely harmless, the interiors of the cans of thelower rate of heat transfer in glass as compared with metallic containers, the milk can be heated to a higher temperature and in a shorter periods! .time by the use 0! suitable agitating ance with the present methods of sterilizing milk in tin cans. The combination of the use of glass bottles, together with the novel method of rapidly heating the milk to sterilizing temperature results in evaporated milk having superior flavor and appearance and, therefore, greater appeal to the consumer.

An object of this invention, therefore, is to provide a process of sterilizing evaporated milk in glass bottles.

Other objects of the invention will become apparent from the description hereinafter of typical methods embodying the present invention.

The milk may be concentrated or evaporated in accordance with any of the prior methods, but we prefer to concentrate or evaporate the milk in the manner disclosed in our copendlng application Serial No. 381,552, filed March 3, 1941, now Patent No. 2,372,239, dated March 2'7, 1945 for the reason that the product obtained thereby is superior in heat stability to evaporated milk produced by other methods.

In accordance with the disclosure of our Patent No. 2,372,239, the evaporated milk product is prepared by means of a closelyrelated series of steps which include, generally, the forewarming of the milk at a comparatively lowtemperature (below 200 F.) preparatory to concentrating'the milk so that the amount of protein which is coagulated is decreased. Under these condition high visand heating apparatus, than is possible in accord- After the milk has through the forewarming stage, it is drawn into a vacuum pan where moisture is'evaporated from the milk. The

evaporated milk is then withdrawn from vac-.1 uum pan, delivered toa homogeniser, thence to a collector and then delivered to a bottle filler beneath which the bottles are conveyed. The evap orated milk may be heated prior to its introduction into the bottles or may beintroduced there'- into at substantially room temperature or cold at a temperature between 85 and 45 F., as may be desired. 2

During all oi the operations subsequent to evaporation of the milk. tlie milk is maintained in an atmosphere of inert gas or under vacuum in order to reduce the tendencyof the flavor of the milk to be altered by oxidation. t

when the sterilizing conditions are I caramelizatlon occurs in evaporated milk, certain compounds are formed which-act as anti-oxidants preventing oxidation of susceptible constituents in the product during prolonged storage. At the same time, reactions occur which bringabout the combination of oxygen with constituents or the milk, thereby rendering the product essentially free from oxygen. 9

When milk is sterilized in accordance with the I present invention, caramellzation and the recosity will beobtained when the concentrated milk is subsequently subjected to the sterllizin operation. 7

action involving the formation of the anti-oxidants and the removal of oxygen do not take place and there develops in this product on prolonged storage a flavor best described as oxidized" unless special precautions are taken to avoid it. These precautions are, as described above, the removal of substantially all of the oxy en from the bottle short period of time to a high sterilizing tempem ture and then as quickly as possible cooling the milk without holding it at the sterilizing tem-,

tation of the milk. This head space may be evacuated or may be filled with inert gas. Although various methods 0! and apparatus for agitating the milk may be employed, the most desirable type of agitation may be provided by such that (l) rotation of the bottle about its geometric axis, or (2) about an axisparallel to but not coaxial with the geometric axis of the container. At lower speeds, the second-mentioned method is somewhat more efllcient than the first. However. the second method is limited as to speed of rotation that can be employed without causing foaming and burning of the milk on the walls of the containers. As the speed or rotation is increased in the second method, a speed is reached the center of the bottle. This causes the milk to foam and also prevents free washing of the sides of the bottle with the milk; These difllculties are overcome at higher speeds byrotatlng the bottle about its own axis.

It has been found possible to destroy resistant bacterial spores that may be present in the milk by subjecting the bottled milk, under the conditions of agitation described, to temperatures of 280 F. to 300 F. for periods of 3 to' 5 minutes, the flnal maximum temperature reached in the center ofthe bottle being in the range of 255 F. to 265 F. The more rapidly the temperature is raised to this-critical sterilizing range and the faster the cooling, the less the'flavor of the milk is aifected.

The temperature of the milk, after sterilizing temperature has been attained, is reduced rapidly by subjecting the container to the action of a cooling liquid while maintaining the bottle under an increased pressure in order to prevent the bottle from rupturing or having its cap blown oiI. Preferably, the temperature of the cooling liquid is reduced in stages in order to avoid cracking of the bottles.

Milk processed as described above, possesses several characteristics which distinguish it from milk processed by conventional methods of. ster-. ilization in which the milk is heated at lower temperatures but for longer periods oftime.

One of the most importantcharacteristics of the milk produced in accordance with the present invention is the improved. flavor. Because of the rapidity of heating, there is little, if any. of

the 'caramelization which imparts the typical in. longitudinal section of a typical form of device for sterilizing the evaporated milk.

As shown in the drawing, the apparatus for sterilizing the milk may consist of an autoclave ber I. also has a blowofl 2| for condensate.

In the center of the reel I I is a compartment valve 20 and" an outlet n in which the bottles 2: are" received so that and the compartment 22. I

or pressure chamber It in which is rotatably mounted a reel ll having a multiplicity of perforations i2 therein. The reelis supported upon a shaft it which passes through the end wall ll of the pressure chamber 10 and is driven by a motor. not shown. The chamber i0 has'a door II at one end thereof by means of which it may In the bottom portion of the chamber II is located a manifold. I! to which steam is supplied by means of a pipe i1; Water and compressed air are supplied to the chamber II by means oi ships ll having a valve is therein. The chambe sealed to withstand substantial internal pressure.

The reel is normally driven at about 50 to 200- revolutlons per minute when the compartment 22 is-being used, or between 25 and 75 revolutions per minute when the space between the reel ii and the compartment 22 is used. i

In operation, the bottles which have been filled with evaporated milk produced as disclosed in our application Serial No, 381,552 and sealed are placed in the center compartment 22 of the reel I l.

and/or filled with-an inert or non-oxidizing gas.

Vacuum sealing is particularly satisfactory, and,

because of the rigidity of the glass containers, can readilybe used without causing the containers to collapse during sterilization. As above indicated,

the bottles may be either steam or vapor sealed or may be sealed under reduced pressure. For example, 16 fluid ounces of evaporated milk, measured at 60 F., may be filled into a bottle having an overflow capacity of 17 fluid ounces.-

When the bottles 23' are positioned in the reel II, the door It is closed and the autoclave is sealed. Steam at a temperature between about 280 Rand 300 F. is introduced into the chamber while the bottles are rapidly rotated in the reel ii. ,By using steam at this temperature, the temperature of the milk, measured at the center of a bottle holding 16 fluid ounces, is raised to between 255 and 265 F. in a period'of not over cooled by shutting oi! the steam and introducing a cooling liquid and compressed air into the auto clave. Introduction of air under pressure is essential in order to prevent the bottles frombursting or having their seals blown out.

When using ordinary glass bottles, it is usually necessary to reduce the temperature of the bottles in stages so as to prevent cracking ofthecontainers. A suitable cycle isas follows: -A cooling medium at a temperature of about 145 F. is

introduced into the autoclave and allowed to remain there for about 1 /2 minutes. A secondary cooling medium ata temperature of'about 110 F. is introduced into the autoclave and is allowed to remain in the autoclave for about one minute.

Then a cooling medium at 60 F. is introduced and allowed to remain in the autoclave for a period of abouts minutes. In thls way, the temperature diflerential between the sterllizedmilk and the cooling medium is maintained sufllciently small to prevent cracking of the container.

When heat resistant glass bottles are used, the milk may be cooled by introducing. warm water (about F.) into the autoclave, followed by cold water or even refrigeration.

The extremely short period of heating, even at the high temperature indicated, prevents caramelization or cooking of the milk and thus undesirable flavoring of the milk is avoided.

The bottles are not completely fllled with, milk, but a head space is left which is evacuated 255 and 265 F.

" highly desirable characteristics. a

product which has many novel characteristics, namely, a iresh miik flavor, a white or creamy colon-a high viscosity andv other characteristics vsimilar-toi!reshmilk,suchastheabilitirtobe'l flll ted with rennet and whipped like ii subjected to a heating and chilling before whipping. Moreover, the product is contained in glass which is a most desirable type of container. ior miik, allowing the customer to view the product. e

n been found desirable to store the finished product at a temperature between 50 and 33' 1".

in order to minimize the formation of undesirableflavor therein, ii the bottles of sterilized milk are to be stored for relatively long periods 01' time.

Ifthemilkistobeusedwithinashortperiodoff time. approximately one month, it is unnecessary to. store it at low temperatures, inasmuch as it has been found that undesirable flavors do not: delop in this short period'oi time.

{mm the foregoing description of a a typical embodying the invention and the resulting product, it will be apparent that milk products made in accordance with the present inventionlmay be readily distinguished from rior products because oi the above-noted n'ov I Itwill be understood, or course. that the apparatus used in practicing the process may be varied theme-described example is illustrative only andshouldnotbeconsideredaslimitingthescope "otthe'i'ollowingclaims.

We claim:

.LAmethodoisterllixingevaporatedmilk'in a glass bottle,'-whi'ch comprises preheating evapto about, 130' l".. rotating a bottle containingsaidpreheaudmiikinahorisontalpoeition while heating and maintaining imder super-' ,atmoaphericpress'urethebottletoraisethetem-- to-betweenabout265"and m'llinapericdnotexceedingiiveminuteaandimmsdiateiycooiingsa'idbottleinltasesbycontactingitwithiiuidsoipmsresiiveiydecreasing temperatures; the diiierence in temperaturesmad'in cooling being insuiheientto v assafios The above-described operation produces a 15 than said first fluid.

, 3. A method oi sterilizing'evaporated milk in 80 without departing iron: the inven tion, Accordingly. it should be understood that bottle, rotating said bottle in a ho glass bottle with evaporated milk% sealing the atmospheric pressure at a high to raise the tempera I I tween about 255 and 265 1''. in a period notex- -cee ding ilveminutes. and then. rapidly mp'erature-sufllciently 19 said bottle under superatmospheric pressure by contacting said bottle with 1) a first fluid having' a temperature less than the temperature oi said milk and sumciently m n to prevent c'racking of the bottle and (2) a second fluid cooler a glass bottle which comprises filling a alassbottle partially with evaporated milk, rotstina' said bottle in a horizontal position and about Maw- 20. metric axis at about 50 to 200 revolutions per minute, contacting the bottle while rotating with ailuid under pressure at a temperature between about 280' and 300' I to'raise the temperature oi the milk to between about 255 and 2651". in a :5 period not exceeding about five minutes, and

innne'diatelv rapidly cooling said bottle in a plurallty or decreasing temperature stages nder super-atmospheric pressure.

"4. A method or sterilizing, y erms mm: in ating evaP a glass bottle; whichcompriseshe rated milk to a temperature 6! about 130 F., rotating a bottle containing the heated milk at a speed or 150 to200 R.;P. ii /in a horizontal position while heating the bottle and maintaining it under supcratmospheric pressure to raise the temperature oi'the milk to between about 255' and 265' 1''. int period not exceeding three ininand immediately contacting said'bottle with I a cooling fluid-at a temperature sufliciently high to avoid cracking said bottle andat superaunos'-" f pherlcpressuretored thetemperature oisaid kandthereaitercoolinasaid-milktoalower ROBERT 1. mt I 2. a method of sterilizing meme in v a glass bottle. which com-prises partially iilling-a tion while contacting it with a fluid under super-.

oith'emilktobe-.

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